As electronic components are becoming smaller and smaller along with the internal structures in integrated circuits, it is becoming easier to either completely destroy or otherwise impair electronic components. In particular, many integrated circuits are highly susceptible to damage from the discharge of static electricity. Generally, electrostatic discharge (ESD) is the transfer of an electrostatic charge between bodies at different electrostatic potentials or voltages, caused by direct contact or induced by an electrostatic field. The discharge of static electricity, or ESD, has become a critical problem for the electronics industry.
Device failures resulting from ESD events are not always immediately catastrophic or apparent. Often, the device is only slightly weakened but is less able to withstand normal operating stresses. Such a weakened device may result in reliability problems. Therefore, various ESD protection circuits are typically included in circuits to protect its various components.
Silicon Controlled Rectifier (SCR) or thyristor devices are commonly used for Electrostatic-Discharge (ESD) protection. On one hand, the SCR provides a compact and effective structure for conducting the very large currents that are associated with ESD events. One the other hand, SCR devices are prone to high leakage currents, particularly at high temperatures, high latchup sensitivity due to low holding voltages, and high triggering voltages.
A transistor's physical size limits the voltage that the transistor can withstand without being damaged. Therefore, as the geometries of the transistors that make up integrated circuits are reduced, there is a corresponding reduction in transistor breakdown voltage. As such, the high triggering voltage of the SCR device poses a difficulty in providing ESD protection for densely populated integrated circuits. Furthermore, as semiconductor circuits become more targeted toward very low power and low voltage applications, however, the high leakage currents associated with SCR devices poses difficulties with power sensitive applications.